Something I noticed, but never until now confirmed was that the background artwork seemed to change.
Every time you activate a score multiplier, the background picture changes.
I even managed to activate an 8x multiplier! Really close to the end of the game, with the free multiplier boost active, so that’s why the final image was taken during the last hurrah. RAINBOWS!

Finally, the artwork is noticed! :)

Update: I managed to get a screenshot of the rainbows while they were still nice and bright! yay!